On 2 January 2014 09:15, Jason Resch <jasonre...@gmail.com> wrote: > Edgar, > > I believe I may understand your point about a universal present, but it is > something relativity handles, as far as I can see, without having to > postulate anything new. Anything having the same (x, y, z, t) coordinates > can interact, where t is coordinate time. It seems like you believe that > because the twins are different ages (in different proper times), that they > cannot interact. But they can, because each has traced exactly 10 light > years through space-time (their coordinate times are the same). > > So you might say everything with the same coordinate time, at the same > place (x, y, z) the same, shares a present moment. But you cannot use this > fact to extrapolate to spatially separated things sharing a present. For > this, the definition of a present (what things exist having the same > coordinate times) differs in different reference frames. >
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